Microcoryne cf. cephalata Bengtson

Kouchinsky, Artem, Alexander, Ruaridh, Bengtson, Stefan, Bowyer, Fred, Clausen, Sébastien, Holmer, Lars E., Kolesnikov, Kirill A., Korovnikov, Igor V., Pavlov, Vladimir, Skovsted, Christian B., Ushatinskaya, Galina, Wood, Rachel & Zhuravlev, Andrey Y., 2022, Early-middle Cambrian stratigraphy and faunas from northern Siberia, Acta Palaeontologica Polonica 67 (2), pp. 341-464 : 444-446

Microcoryne cf. cephalata Bengtson in Bengtson et al., 1990

Fig. 74I, K, Q, R, T, V, Z .

Material.—Several tens of phosphatised spicules, including figured SMNH Sp11479–11485, from samples 19/10.25, 19/11.75, and 19/12.75, Erkeket Formation, Khorbusuonka River and from sample 22/0, Tyuser Formation, Lena River. Siberia, Russia; lower Botoman stage (correlated with the lower part of Cambrian Stage 4).

Description.—Mace-shaped phosphatised polyactinal spicules, up to 1 mm long and 0.4 mm wide, consisting of a tuberculated or spinose head and an axial (proximal?) ray. The axial ray is 70–130 µm in diameter and reaches 0.7 mm in length, but may be indistinguishable in some forms ( Fig. 74I ). Up to three (in the available specimens) elongated and pointed paratangential rays are inclined towards to the axial ray, at ca. 30º ( Fig. 74Q ). They are slender and shorter than the axial ray and radiate from a common part of spicule, the head. The entire surface of the head is covered with numerous short blunt tubercles and longer spines. They tend to be radially grouped in 3–4 circlets, but may also be disorderly arranged on the entire head surface ( Fig. 74Z ). The spicules, now phosphatised, consist of aciculate longitudinally aligned elements.

Remarks.—Bengtson et al. (1990) suggested that these microfossils from the Cambrian Series 2 of South Australia can belong to octocorals, based on their microstructure of acicular needle-shaped radiating crystals. Similar spicules were reported from other parts of Gondwana, such as Germany and Jordan (Elicki 1994, 2011) and occur through the Cambrian Stage 3–Miaolingian Series. These microfossils are also ascribed to heteractinid spicules ( Kouchinsky et al. 2015a). Peel (2019: fig. 4A, J) suggested sponge affinities based on the presence of axial canal in a single specimen of Microcoryne sp. found in the Cambrian Stage 4 of North Greenland. If high morphological variability of Microcoryne is not taken into consideration, formal genera and species are described such as Conwaymorrisispongia bengtsoni ( Kozur et al. 2008) , which type material even is derived from the type localities of Microcoryne cephalata (Bengtson et al. 1990) . Some spicules may also be thickened by a secondarily phosphatised mass consisting of aciculate elements with a probably originally aragonitic composition ( Fig. 74T ). We interpret such spicules as belonging to heteractinids with originally aragonitic polycrystalline composition and occasionally aragonitic cement overgrowth.

Heteractinid elements co-occur in the lower Botoman samples with fragments of archaeocyaths represented by phosphatised infills of canals in the walls ( Fig. 78A–G ) and with presumably eroded and rounded fusiform fragments of polyactinal spicules ( Fig. 78H–P ).

Figures

Fig. 74. Heteractinid spicules from the lower Cambrian Erkeket Formation, Khorbusuonka River (A–E, G, I, K–Q, V, Y) and Tyuser Formation, lower reaches of the Lena River (F, H, J, U, W, X, Z), Siberia, Russia; samples 11/16.05 (Y), 19/10.25 (E, I, K, L, O–Q), 19/11.75 (A–D, R–T, V), 19/12.75 (G, M, N), 21/21 (U, W, X), and 22/0 (F, H, J, Z). A–H, J, L–P, S. Polyactinal spicules with an axial ray, SMNH Sp11460–11474, respectively. U, W–Y. Inflated polyactinal spicules from the Tommotian Stage, SMNH Sp11475–11478, respectively. I, K, Q, R, T, V, Z. Microcoryne cf. cephalata Bengtson in Bengtson et al., 1990, SMNH Sp11479–11485, respectively.Scale bar: 250 µm (A–J, N, O, Q, R, V,Y, Z) and 500 µm (K–M, P, S, T, U, W, X).

Fig. 78. Sponge fragments from the lower Cambrian Erkeket Formation, Khorbusuonka River (A–F, H, I, M, N) and Tyuser Formation, lower reaches of the Lena River (G, J–L, O, P), Siberia, Russia; samples 19/10.25 (B–F, M, N), 19/11.75 (A, H, I), and 22/0 (G, J–L, O, P). A–G. Fragments of archaeocyaths, SMNH Sp11519–11525, respectively. H–P. Fragments of possible heteractinid spicules, SMNH Sp11526–11534, respectively. Scale bar: 250 µm (A, C) and 500 µm (B, D–P).